The present invention relates generally to the field of camera imaging. Embodiments of the present invention relate more specifically to the fields of gamma camera imaging, handheld cameras, and surgical imaging.
A handheld gamma ray camera is a nuclear medicine device used for close proximity imaging of radioactively labeled tracers that are injected into the body. An exemplary application of such a camera is surgical cancer staging.
Cancer staging is a process where tests are performed to determine, after a primary tumor has been diagnosed, if cancer cells have spread locally or throughout the body. Staging of breast cancers and melanoma often requires lymphatic dissection and pathology. A technique called a sentinel node (SN) procedure attempts to locate the “sentinel” lymph node, or the closest lymph node of the lymphatic system that directly drains the tumor basin. In this procedure, just that one sentinel node is located and removed. This process is an alternate procedure to conventional lymph node dissection that reduces the invasiveness and complications of the surgical biopsy procedure. The sentinel lymph node is a good indicator of cancer invasiveness; if the sentinel node is clear of cancer cells then it is unlikely that the cancer is actively spreading.
In an exemplary surgical cancer staging procedure, illustrated in FIG. 1, a surgeon injects a radioactive substance (a tracer) 10, a blue dye, or both into the area around a primary tumor site 12. An exemplary tracer is radioactive Tc-99 m Sulfur Colloid, having a large particle size (appr.100-500 nm). Lymphatic vessels 14 carry the tracer 10 to the first lymph node (sentinel node) 16 into which the area drains; this is the lymph node most likely to contain cancer cells. This procedure helps to “map” the drainage pattern of lymphatic fluid from the skin to the lymph nodes. Such a map may help to show the direction the cancer is likely to spread and the lymph node most likely to contain cancer cells. The surgeon can either visually identify the blue dye or detect the tracer 10 by detecting the presence of radiation from the tracer. The lymph node 16 can then be removed for examination under a microscope (pathology).
One method of detecting the tracer 10 uses non-imaging intra-operative gamma detecting probes, which produce a sound proportional to counts that are detected near a tip of the probe. However, because the tracer distribution is heavily concentrated at the injection site, and only a few percent typically ever drains into the lymph nodes, a non-imaging probe can be easily confused by the injection site, and significant training and experience are needed to avoid this complication.
Another method of tracer detection uses a gamma ray camera, such as a fixed or handheld gamma ray camera. As opposed to the non-imaging probes, a handheld gamma ray camera can help the localization of lymph nodes, because it can give a surgeon real-time visual cues as to tracer distribution relative to the injection site. However, problems arise with the use of handheld gamma ray cameras that may result in poor images or complex operation.
For example, handheld gamma ray cameras suffer from low statistical quality image data. In gamma ray imaging, tracer quantities of the radioactive substance and relatively low photon count sensitivity of gamma ray collimators may mean only a few counts are collected by the imaging surface of the detector. Additionally, blurring artifacts can result when the gamma ray camera is scanned across the field of interest. For instance, hand-motion of the gamma ray camera during use (e.g., during a surgical biopsy procedure) will blur active objects within the field of view.
There are competing technologies that attempt to solve problems associated with a moving gamma ray camera. One general solution uses motion detectors to synthesize a large field of view. An exemplary method attempts to perform tomography by tracking the spatial location (derived by absolute motion and position sensor) of the gamma ray camera, forming limited angle projections, and then backprojecting these into some form of tomographic image or planar tiled image. This technique, however, has significant limitations in the reconstructed resolution of the system (e.g., often >10 mm). Slight misidentification of the absolute position and rotation of the camera typically results in large blurring effects and streaks on the reconstructed image.
In another compensation method, blurring artifacts may be removed by manual intervention by selectively clearing a current acquisition frame, such as by operating a pedal while manipulating the camera. However, such an operation can be burdensome for the camera operator, and in many cases will require a separate person. For example, a known practice uses a dedicated technician who controls the acquisition. The surgeon must give verbal commands to the technician to clear the current frame.
As another alternative, a fixed high frame rate may be used to reduce motion-blurring artifacts. However, in this case, many events are thrown away and poor statistical quality images are formed from the relatively few events that are captured.
Thus, known compensation methods insufficiently address the above-described problems. Such problems have resulted in continued use of non-imaging probes for surgical cancer staging, in spite of the benefits of gamma cameras.